Last fall, Wall Street Journal wrote (and AdLab blogged) about how advertisers were injecting ads into peer-to-peer networks used to trade pirated wares. Now Ars Technica brings more details in its tour of Media Defender:

"Last year, the company partnered with Jay-Z and Coke in a widely-covered promotion that saw MediaDefender pushing a legitimate piece of Jay-Z concert footage to fans who searched for videos by the artist. In essence, these are "decoys" that contain real content. The company has also helped promote Vitamin Water commercials that were deemed too "edgy" for network television, along with video game trailers and exclusive P2P remixes.

Some of [the] small firms have actually paid MediaDefender to serve content by their acts, often in response to users searching for a related (but better known) artist."